The present invention relates in general to semiconductor devices and, more particularly, to high current, high voltage bidirectional switching devices.
Bidirectional switches are power devices that switch high currents through their conduction electrodes while blocking high voltages applied to the conduction electrodes. Bidirectional switches are used in a variety of electrical systems. For example, battery chargers often use a bidirectional switch to control a current flowing between a terminal of the charger to a terminal of a battery being charged. A control voltage is applied to a control electrode of the bidirectional switch to close the switch and allow current to flow from the charger terminal to the battery terminal to charge the battery. When the control voltage is removed, the bidirectional switch opens and no current flows. If the charger is turned off while the battery is attached, the switch blocks the voltage on the battery terminal, and if the battery is removed while the charger is turned on, the switch blocks the voltage on the charger terminal. A typical bidirectional switch is specified to supply at least one ampere of current while blocking voltages of at least eight volts without breaking down.
Standard planar power metal-oxide-semiconductor field effect transistors (MOSFET) are not adequate for use as bidirectional switches because they have low gate to source breakdowns, often as low as five volts, and have a low current capability due to low packing density for a given breakdown voltage. Standard vertical power MOSFETs also are not adequate because of a low breakdown in one direction, making them unidirectional devices. Consequently, current bidirectional switches typically are implemented using two separate serially coupled power MOSFETs, with the drain of each transistor operating as a conduction electrode of the switch. The separate MOSFETs are formed on separate semiconductor dice and housed in separate packages, which results in a high manufacturing cost and a large area occupied on a circuit board. When the separate MOSFET dice are housed in a single package and interconnected with wire bonds, the area occupied on a circuit board is reduced but the manufacturing cost is still too high for many applications.
Hence, it would be a benefit if there were a bidirectional switch that was manufactured on a single semiconductor die in order to reduce the manufacturing cost of the bidirectional switch.